Mangroves: Trees in Salt Water
Most trees die if their roots sit in salty water, but mangroves thrive along tropical coasts, where the tide rises and falls around their trunks. Mangroves have several ways of coping with salt. Some species block much of the salt at the roots, others take it in and push it out through glands on their leaves, which can leave white crystals on the surface, and a few store salt in old leaves that later drop.
The mud in a mangrove forest holds very little oxygen, so the roots need another way to breathe. Many mangroves grow roots that rise above the mud. Some of these look like stilts, and others look like small pencils pointing upward, called pneumatophores, which take in air when the tide is low.
These tangled roots do important work. They slow incoming waves and help protect the shoreline from storms and erosion. They also trap sediment, which can build up land over time. Among the roots, young fish, crabs, and shrimp find shelter, so mangroves act as nurseries for sea life, and many coastal families depend on the fish that begin life there.
Mangrove seeds are unusual as well. In some species, the seed begins to grow while it is still attached to the parent tree, forming a long, slender seedling called a propagule. When it drops, it can float on the water for a long time before it lodges in the mud and takes root, so the tide helps the young trees spread to new shores.
In many regions, mangrove forests have been cleared for farms, shrimp ponds, and buildings. Because the forests are so valuable, many communities now work to protect the ones that remain and to plant new ones.